1. Field of the Invention
The present invention relates to a bearing provided with a rotation sensor, and more specifically, it relates to the structure of a bearing employed for a general-purpose motor requiring a rotation detecting function.
The present invention also relates to a bearing provided with a rotation sensor, and more specifically, it relates to a method of extracting a signal from a bearing provided with a rotation sensor.
The present invention further relates to a bearing provided with a rotation sensor, and more specifically, it relates to a bearing provided with a rotation sensor having a function of detecting the number of rotations or a rotational direction.
The present invention further relates to a bearing provided with a rotation sensor and a motor employing the same, and more specifically, it relates to a bearing provided with a rotation sensor supporting a shaft requiring a rotation detecting function. More particularly, the present invention relates to a bearing provided with a rotation sensor used in the vicinity of a general-purpose motor or the like generating a large magnetic field.
2. Description of the Prior Art
First Prior Art
The structure of a bearing 500 provided with a rotation sensor according to first prior art is described with reference to FIG. 26. FIG. 26 is a sectional view showing the structure of the bearing 500 provided with a rotation sensor. This bearing 500 provided with a rotation sensor, forming an antifriction bearing, comprises an outer ring 1, an inner ring 3 and rolling elements 2. A shielding member is provided between the outer ring 1 and the inner ring 3.
When the inner ring 3 is employed as a rotating bearing ring, a pulser ring 4 is fixed to the inner ring 3 with a mandrel 5. When the outer ring 1 is employed as a fixed bearing ring, a magnetic sensor 8 is fixed to the outer ring 1 with a sensor case 7 and a sensor case fixing ring 6. The bearing 500 provided with a rotation sensor having the aforementioned structure, which is compact and strong with no requirement for assembly control, is applied to a support bearing for the rotary shaft of a motor.
Problem of First Prior Art
FIG. 27 shows the bearing 500 provided with a rotation sensor having the aforementioned structure in a state assembled into a motor. FIG. 27 is a sectional view showing the structure of the motor into which the bearing 500 provided with a rotation sensor is assembled. A motor rotor 11 assembled into a rotary shaft 12 is supported in a housing 13 by a front bearing 14 and a rear bearing 15, and a motor stator 10 is also fixed to the housing 13. In the motor shown in FIG. 27, the rear bearing 15 stores a rotation sensor.
When a large current is fed to the motor stator 10, the flow of a magnetic flux cannot be ignored. A magnetic loop is generated to pass through the motor rotor 11, the rotary shaft 12, the inner ring 3, the outer ring 1 and the housing 13 and return to the motor stator 10 as shown by arrows in FIG. 27. At this time, a nonmagnetic part occupies most part of the space between the inner ring 3 and the outer ring 1, except the rolling elements 2. The magnetic rolling elements 2 are in point contact with the inner ring 3 and the outer ring 1, and arranged only on about six portions of a circumference. Therefore, a path through the inner ring 3, the rolling elements 2 and the outer ring 1 has high magnetic resistance.
Consequently, the bearing 15 exhibits high magnetic resistance, readily leading to leakage of a magnetic flux. The leaking magnetic flux flows to the sensor case fixing ring 6 and the mandrel 5, which are magnetic members, to disadvantageously exert bad influence on the magnetic sensor 8 and disturb a sensor signal.
Second Prior Art
Another type of bearing provided with a rotation sensor has a rotating element provided with a sensor target such as a magnetic pattern and a fixed element provided with a sensor element for detecting relative rotational movement of the sensor target with respect to the sensor element and outputting an electric signal.
FIGS. 28 and 29 show the sectional structures of bearings 600a and 600b provided with rotation sensors according to second prior art. Each of the bearings 600a and 600b provided with rotation sensors has an inner ring 601, an outer ring 603 and rolling elements 602 provided in an annular space defined between the inner ring 601 and the outer ring 603. When the inner ring 601 is employed as a rotating element, an encoder ring 604 serving as a sensor target is fixed to the inner ring 601. When the outer ring 603 is employed as a non-rotating element, a rotation detecting sensor 605 detecting rotation of the encoder ring 604 is fixed to the outer ring 603.
Problem of Second Prior Art
In order to extract an output signal from the rotation detecting sensor 605, a cable must be extracted from a circuit board into which the rotation detecting sensor 605 is assembled. When the outer diameter of the bearing 600a or 600b is larger than 30 mm, a cable 610 can be extracted from an axial end surface of the bearing 600a provided with a rotation sensor as shown in FIG. 28 or from the outer peripheral surface of the bearing 600b provided with a rotation sensor as shown in FIG. 29.
If the outer diameter of the bearing 600a or 600b is smaller than 30 mm, however, no space for extracting the cable 610 is defined but it is difficult to extract a signal from the rotation detecting sensor 605.
Third Prior Art
FIG. 30 is a sectional view showing a bearing provided with a rotation sensor according to third prior art. Referring to FIG. 30, this bearing provided with a rotation sensor is an antifriction bearing formed by an outer ring 701, an inner ring 703 and rolling elements 702, and a pulser ring 704 is fixed to the rotating element (the inner ring 703, for example) while a magnetic sensor 705 is fixed to the non-rotating element (the outer ring 701, for example) through a sensor case 706. A magnetic encoder is formed on the surface of the pulser ring 704. Such a bearing provided with a rotation sensor, which is miniature and strong with no requirement for assembly control, is utilized for supporting a motor or the like.
Alternatively, the outer ring 701 and the inner ring 703 may be employed as a rotating element and a non-rotating element respectively.
The sensor of such a bearing provided with a rotation sensor generates an analog output shown in FIG. 31A or a rectangular wave output shown in FIG. 31B. An analog output type sensor must have repetitive reproducibility of a sinusoidal waveform, and hence uniformity of magnetization intensity is important for the magnetic encoder. A rectangular wave output type sensor utilizes an output signal in a saturated waveform, and hence large magnetization intensity is more strongly required as compared with uniformity of the magnetization intensity. When the magnetization intensity is large, magnetic field strength steeply changes to advantageously improve pitch accuracy or increase a sensor gap.
Problem of Third Prior Art
In general, anisotropic magnetic powder is employed for the magnetic encoder regardless of the output signal. When anisotropic magnetic powder is employed for an analog output type encoder, however, the amplitude of a sinusoidal wave output is disadvantageously largely dispersed.
Fourth Prior Art
FIG. 32 is a longitudinal sectional view of a bearing provided with a rotation sensor according to fourth prior art. Referring to FIG. 32, the bearing provided with a rotation sensor is an antifriction bearing formed by an outer ring 801, an inner ring 803 and rolling elements 802, and a pulser ring 804 is fixed to a rotating side (the side of the inner ring 803, for example) through a mandrel 805 while a magnetic sensor 808 is fixed to a non-rotating side (the side of the outer ring 801, for example) through a sensor case 807 and a sensor case fixing ring 806. Such a bearing provided with a rotation sensor, which is miniature and strong with no requirement for assembly control, is employed as a bearing for supporting a motor or the like.
Problem of Fourth Prior Art
When the bearing provided with a rotation sensor shown in FIG. 32 is assembled into the magnetic path of a coil or a magnet generating a large magnetic field, however, an output of the bearing provided with a rotation sensor may malfunction by a leakage flux caused by the external magnetic field.
FIG. 33 shows the bearing provided with a rotation sensor assembled into a motor, for example. Referring to FIG. 33, a front bearing 814 and a rear bearing 815 provided with a rotation sensor support a motor rotor 811 assembled into a rotary shaft 812 in a housing 813, to which a motor stator 810 is fixed. When a large current is fed to the motor stator 810, the flow of a magnetic flux cannot be ignored but a magnetic loop is generated to pass through the motor rotor 811, the rotary shaft 812, the inner ring 803, the outer ring 801 and the housing 813 and return to the motor stator 810 as shown by arrows in FIG. 33.
When the direction of the current is reversed, the magnetic loop is also reversed. At this time, a nonmagnetic part dominantly occupies the space between the inner ring 803 and the outer ring 801 except the rolling elements 802 and a retainer 819 and to increase magnetic resistance, and hence a magnetic flux readily leaks to influence the magnetic sensor 808 and disturb a sensor signal or cause a malfunction.
A first object of the present invention is to provide a highly reliable bearing provided with a rotation sensor exerting no bad influence on a magnetic sensor, in order to solve the aforementioned problem of the first prior art.
A second object of the present invention is to provide a bearing provided with a rotation sensor capable of readily extracting a signal from a rotation detecting sensor also when the outer diameter thereof is smaller than 30 mm, in order to solve the aforementioned problem of the second prior art.
A third object of the present invention is to provide a bearing provided with a rotation sensor employing isotropic magnetic powder for an analog output to be capable of reducing dispersion of the amplitude of a sinusoidal wave output, in order to solve the aforementioned problem of the third prior art.
A fourth object of the present invention is to provide a bearing provided with a rotation sensor capable of cutting off a loop of a leakage flux flowing to a magnetic sensor and reducing influence on the magnetic sensor and a motor employing the same, in order to solve the aforementioned problem of the fourth prior art.
A bearing provided with a rotation sensor according to a first aspect of the present invention comprises an inner ring, an outer ring and a plurality of rolling elements stored between the aforementioned inner ring and the aforementioned outer ring and stores a sensor detecting the rotational speed of a rotor, and further includes a pulser ring mounted on a first end of a rotating bearing ring formed by either the aforementioned inner ring or the aforementioned outer ring, a sensor mounted on a first end of a fixed bearing ring formed by the remaining one of the aforementioned inner ring and the aforementioned outer ring on a position opposed to the aforementioned pulser ring and a magnetic ring mounted on second ends of the aforementioned inner ring and the aforementioned outer ring for forming a magnetic path between the aforementioned inner ring and the aforementioned outer ring.
In the bearing provided with a rotation sensor according to this aspect, leakage of a magnetic flux can be prevented in a bearing part by arranging a magnetic body between the outer ring and the inner ring and reducing magnetic resistance in the bearing part. Consequently, a magnetic sensor is prevented from bad influence exerted by leakage of the magnetic flux, and the bearing provided with a rotation sensor can be improved in reliability.
In the aforementioned aspect, the aforementioned magnetic ring is preferably a seal sealing an annular space defined between the aforementioned inner ring and the aforementioned outer ring. More preferably, the aforementioned seal is a rubber seal containing magnetic powder. According to this structure, the magnetic ring can be provided with a function of forming a magnetic path between the aforementioned inner ring and the aforementioned outer ring and a function of sealing the annular space defined between the aforementioned inner ring and the aforementioned outer ring.
In the aforementioned aspect, the aforementioned magnetic ring is preferably provided with an outwardly directed projection. Thus, when the bearing provided with a rotation sensor is applied to a bearing for the rotary shaft of a motor, a detent for the fixed bearing ring can be implemented by engaging the projection with a housing of the motor.
In the aforementioned aspect, the bearing provided with a rotation sensor preferably further comprises a sensor case holding the aforementioned sensor, a sensor case fixing ring fixing the aforementioned sensor ring and a mandrel holding the aforementioned pulser ring, and at least either the aforementioned sensor case fixing ring or the aforementioned mandrel is preferably a nonmagnetic member.
When at least either the sensor case fixing ring or the mandrel is formed by a nonmagnetic member as described above, the magnetic resistance of the magnetic sensor part can be so increased that no magnetic flux passes through the magnetic sensor part.
A motor according to the present invention comprises a housing, a stator fixed to the aforementioned housing and a rotor opposed to the aforementioned stator and fixed to a rotary shaft, and employs the bearing provided with a rotation sensor according to the first aspect for supporting the aforementioned rotary shaft.
When the bearing provided with a rotation sensor according to the first aspect of the present invention is employed for supporting the rotary shaft of the motor, a rotation signal of the motor can be correctly obtained.
A bearing provided with a rotation sensor according to a second aspect of the present invention comprises an inner ring, an outer ring and a plurality of rolling elements stored between the aforementioned inner ring and the aforementioned outer ring and stores a rotation detecting sensor detecting the rotational speed of a rotor, and further comprises an electric terminal for coming into contact with an externally provided connection terminal for supplying power to the aforementioned rotation detecting sensor and outputting an electric signal from the rotation detecting sensor.
Thus, no cable may be directly extracted from the bearing provided with a rotation sensor for outputting a signal from the rotation sensor. Consequently, the bearing provided with a rotation sensor can be miniaturized and a space for assembling the same into a housing of a motor or the like can be reduced.
In the aforementioned aspect, the outer diameter of the aforementioned outer ring is preferably not more than 30 mm. In the aforementioned aspect, the aforementioned electric terminal is preferably in the form of a pad. In the aforementioned aspect, the aforementioned electric terminal is preferably in the form of a pin. In the aforementioned aspect, the aforementioned rotation detecting sensor is preferably any of a magnetic sensor, an eddy current sensor or a photosensor.
In the aforementioned aspect, the aforementioned electric terminal is preferably provided on the outer peripheral surface of a sensor case for fixing the aforementioned rotation detecting sensor. In the aforementioned aspect, further, the aforementioned electric terminal is preferably provided on an axial end surface of a sensor case for fixing the aforementioned rotation detecting sensor.
Thus, no space is required for extracting a cable for outputting a signal but the bearing provided with a rotation sensor can be miniaturized and a space for assembling the same into a housing of a motor or the like can be reduced.
In the aforementioned aspect, the bearing provided with a rotation sensor is preferably provided with rotational direction positioning means for positioning the aforementioned connection terminal, which is externally provided, with respect to the aforementioned electric terminal along the rotational direction. In the aforementioned aspect, further, the bearing provided with a rotational sensor is preferably provided with axial direction positioning means for axially positioning the aforementioned connection terminal, which is externally provided, with respect to the aforementioned electric terminal.
Thus, an operation for assembling the bearing provided with a rotation sensor to a housing of a motor or the like can be improved in efficiency, and the electric terminal and the connection terminal can be readily connected with each other by simply assembling the bearing provided with a rotation sensor into the housing.
In the aforementioned aspect, the bearing provided with a rotation sensor preferably further includes at least one of a temperature sensor, a vibration sensor and a load sensor.
A bearing provided with a rotation sensor according to a third aspect of the present invention comprises an inner ring, an outer ring and a plurality of rolling elements stored between the inner ring and the outer ring and stores a sensor detecting the rotational speed of a rotor so that one of the inner ring and the outer ring forms a rotating bearing ring and the other one forms a fixed bearing ring, and further includes a pulser ring mounted on an end of the aforementioned rotating bearing ring and a sensor mounted on the aforementioned fixed bearing ring in opposition to the aforementioned pulser ring. The pulser ring is a magnetized encoder consisting of elastomer containing magnetic powder, and isotropic magnetic powder is employed when the sensor outputs an analog signal while anisotropic magnetic powder is employed when the sensor outputs a rectangular wave signal.
Thus, dispersion of magnetization intensity can be reduced, thereby reducing dispersion of the amplitude of the output from the sensor.
When the encoder outputs an analog signal, an MR element is employed as the sensor.
The magnetic powder is ferrite.
A bearing provided with a rotation sensor according to a fourth aspect of the present invention comprises an inner ring, an outer ring and a plurality of rolling elements stored between the inner ring and the outer ring and stores a sensor detecting the rotational speed of a rotor so that one of the inner ring and the outer ring forms a rotating bearing ring and the other one forms a fixed bearing ring, and further comprises a pulser ring mounted on an end of the rotating bearing ring, a sensor mounted on the fixed bearing ring in opposition to the pulser ring and a magnetic ring arranged between the rolling elements and the sensor in an annular space defined between the inner ring and the outer ring for forming a magnetic path.
Thus, influence exerted by a leakage flux on a magnetic sensor or the pulser ring can be minimized and the sensor can be prevented from disturbance of the waveform of its output or a malfunction, to be resistant against an external leakage flux.
An air gap between the magnetic ring and the rotating bearing ring is selected to be not more than 0.5 mm.
The bearing provided with a rotation sensor further comprises a sensor case holding the sensor, a sensor case fixing ring fixing the sensor case and a mandrel holding the pulser ring, and the sensor case fixing ring and the mandrel are formed by magnetic members.
A magnetic bypass reducing magnetic resistance is provided between the sensor case fixing ring and the rotating bearing ring.
The sensor case fixing ring is formed with a slit on the side of the fixed bearing ring on which the sensor case fixing ring is mounted and in the vicinity of the sensor.
The pulser ring is formed by a magnetized encoder consisting of elastomer containing magnetic powder.
The thickness of the elastomer in the magnetized encoder is at least 2 mm.
Another motor according the present invention comprises a housing, a stator fixed to the housing and a rotor opposed to the stator and fixed to a rotary shaft, and employs the bearing provided with a rotation sensor according to the fourth aspect.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.